1. Field of the Invention
The present invention relates to calibration for gradation correction of a color printer.
2. Related Background Art
In general, in a case where color printing is performed by a color printer connected to a PC (personal computer), a printing characteristic of the color printer changes as time passes, a printed result might resultingly change. Such a change of the printing characteristic is generally called a successive change. The successive change occurs in accordance with temperature, humidity, the reminder of toner being a printing agent, a use frequency of a photosensitive drum, and the like.
As a result, in a case where printing data generated based on a printer characteristic at a certain time is subjected to printing at another time, the printed result of proper color can not occasionally be obtained.
Further, even in a case where plural printers of the same type are used, an individual difference occurs in the printing characteristic between, e.g., a printer A and a printer B because of the above reason, whereby the printed result by the printer A might be different from the printed result by the printer B.
In order to solve such problems, calibration that the printing characteristics of the printers are measured and, e.g., a gradation correction condition is thus rectified (or corrected) is performed.
As an example of the conventional calibration, there is calibration between an engine and a controller which together constitute the printer.
This conventional calibration is automatically performed within the printer irrespective of an instruction by a user or a host computer. Such a process is called device calibration hereinafter. In the device calibration, a latent image for each of C (cyan), M (magenta), Y (yellow) and K (black) is formed on the photosensitive drum, potentials of the formed latent images are measured to obtain the printing characteristic, and the gradation correction condition is thus rectified. It should be noted that, in the device calibration, instead of the latent image formed on the photosensitive drum, the printing characteristic is occasionally obtained by measuring a density of a toner image formed by developing the latent image with toner.
By the above device calibration, the calibration is regularly performed without troubling the user.
However, in the device calibration, characteristics of sensors themselves using the calibration are relatively dispersed, whereby there is no accuracy necessary to be able to ensure the absolute density value by which the individual difference between the printers is excluded. Namely, it is possible to stabilize a relative density characteristic being a density characteristic peculiar to each printer, by suppressing a change in the characteristic due to factors such as temperature, humidity and the like which the change may occur in the printer. However, it is difficult to obtain and stabilize an absolute density characteristic.
On the other hand, one calibration method is disclosed in Japanese Patent Laid-Open Application No. 2000-318266. This is the calibration which is performed, through a user""s operation, between a computer and a color printer together constituting a system. Namely, in response to an instruction from a computer, a patch for measurement is formed on a sheet by the color printer, the sheet is read by a scanner, calibration data is generated by the computer on the basis of patch data read from the sheet, and the generated calibration data is downloaded to the printer. Such a process is called soft calibration. The soft calibration can achieve higher-accurate patch measurement as compared with the device calibration, whereby it is possible to stabilize the absolute density characteristic and greatly reduce the dispersion in the printing characteristics among the plural printers. It should be noted that, in the soft calibration, since the user""s operation is necessary to cause the scanner to read the created patch, a load is put to the user.
Incidentally, there are following problems in the above conventional calibration technique.
Namely, in one of the above two kinds of calibrations, the relative density characteristic can be stabilized, and in the other thereof, the absolute density characteristic can be stabilized. In other words, each calibration has the different merit and demerit. Since these two calibrations respectively function independently, they did not conventionally function with a correlation mutually. Thus, for example, even:if the soft calibration is performed at certain timing to adjust the printing characteristic, the adjusted printing characteristic changes due to the device calibration occurred at predetermined timing, whereby the absolute density characteristic based on the soft calibration may not be maintained. Therefore, in order to obtain the stabilized printed result at any time, the soft calibration to which the user""s operation is-necessary must be performed frequently.
Further, the printing using the above calibration data is limited to a case of a PDL (page description language) mode where the above image process is performed in a printer controller. Namely, in a so-called image mode that all image processes including rasterizing and binarization are performed on a client computer connected to a conventional printing system, the image process which uses the above calibration data can not be achieved.
On the other hand, although the image process using the calibration data can be performed in the PDL mode, the image process using the calibration data can not be performed in the image mode, whereby there is the drawback that a tint of a printed image output in the PDL mode is different from a tint of a printed image output in the image mode.
An object of the present invention is to provide an image processing apparatus and a calibration method which solved the above problems.
Another object of the present invention is to provide an image processing apparatus and a calibration method which can stabilize a printing characteristic as reducing a user""s load by appropriately combining plural calibrations respectively having different merits.
Still another object of the present invention is to provide an image processing apparatus and a calibration method which can obtain a stabilized printing characteristic in any mode by providing even in an image mode a structure of performing calibration same as that in a PDL mode.
Still another object of the present invention is to provide an image processing apparatus and a calibration method which can reduce a load to a network by reducing as much as possible information necessary in the image mode, and can also reduce a load to a process of creating a calibration table in the image mode by obtaining the calibration table itself.
Other objects and features of the present invention will be clarified through the following description in the specification and the attached drawings.